Originally a mud pit consisted of a shallow excavated hole located alongside a vehicle-mounted earth drill. After filling such a pit with fluid, the fluid was pumped through the drill stem into the hole, forced upwards around the drill stem into a canal in the ground through which it flowed back to the pit. The pit provided a controlled area to contain a supply of fluid, a facility from which rock and debris could be observed and removed and a surge vessel for recirculating fluid.
Over time, excavated mud pits have generally been replaced by portable tubs which eliminate excavating and refilling. In addition a portable tub reduces disfiguration of the area as well as water loss into the subsoil. Such tubs are generally carried atop the drill mast when in its horizontal, transport position. Upon arrival at the site for drilling a hole, they are manually lowered to the rear of the drilling apparatus such that an opening in their receiving end surrounds the drill stem. Such portable mud pits may have provisions for sectional screening of the liquid as it moves from the receiving end of the pit to the discharge end. A disadvantage of portable pits is the longer distance between the discharge end and the pump. Fluid must be lifted this additional distance and cavitation may be created in the long flexible suction hose.
Typical mud pits of this type generally range in length from seven to fourteen feet, in width from two to four feet, and in height from one to two feet. Physically, they are impractical for fewer than two persons to handle. Often it is necessary for a third, or even a fourth person to be present at job site when the mud pit is to be loaded or unloaded. Due to its bulk, weight, and unwieldy shape, the portable mud pit is highly susceptible to denting, breaking and bending. Such damage later interferes with liquid flow, causes leaks and hampers the functioning of screens and inlet pipe.
In addition to the mud pit itself, loading and unloading it from the mast subjects the drill and its accoutrements, as well as ancillary equipment and supplies, to frequent and costly damage. Also, care must be taken to be sure over-the-road height limitations are met and there is always a risk that the mud pit will come loose while being transported.